DE. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 4'25 



required by known spectrum laws. It must be remembered that the appearance of 

 the Em lines varies very much in relative intensity with different observers (cf., for 

 instance 4604, 4460 above) that some appear early and then disappear, that others 

 come in after the emanation has stood for a few days, and further that the copper 

 electrodes, which extended the useful duration of the tubes, would probably have some 

 effect on the nature of the emitting sources in the gas. To account for this, the 

 suggestion might be thrown out that the activity of the emanation would by itself 

 ionize the molecules of the gas, and that especially the a-rays would ionize in a 

 different and more drastic way than the ordinary cathode or vacuum tube ionization. 

 That with time the y-rays from the active deposit might ionize in again a different 

 way and produce again new lines. One would expect that the self-effect as it may 

 be called is so drastic that it destroys those configurations which should give the red 

 spectrum analogous to that in the other gases. It is a fact, as I hope to show, that 

 the spectrum, so much as there is of it, is decidedly of the jar, or blue kind. 



The degree of accuracy of the observations is not of the best. KOYD claims an 

 accuracy of O'lA. The spectrum was obtained by a concave grating of 1 metre 

 radius and extended from 5084 to 3005, with some additional lines by a prism 

 spectrograph, subject to errors of '5A. WATSON'S lines extended from 7057 to 3867 

 with several new lines. His degree of accuracy is probably about the same us that of 

 ROYD. In the following we shall treat the maximum errors as '2A except where lines 

 are only given to the nearest unit. 



The extent of the spectrum observed is too restricted to expect to find more than 

 the S(2) and D(l) lines, and even in the case of S (2) the S s (2) and S 3 (2) may be in 

 the violet where only glass apparatus was used. Further, there is the added 

 disadvantage that the links are so large that they can stretch from the unobserved 

 ultra-red to the unobserved ultra-violet, and consequently can only act as sounders 

 for lines so far in the ultra-violet that an e link lands within the visible red. The F 

 lines should be expected to lie wholly in the observed region, and this must be the 

 chief guide in the unravelling of the series relations. 



As a preliminary and definite starting point, we have the value of the oun as 

 calculated from the atomic weight. But here also there is some uncertainty. The 

 value of HONIGSCHMIDTS' determination of the atomic weight of Ra, 225'97 is now 

 generally accepted as close to the real value, as against the earlier value of 226 '4. 

 This makes the atomic weight of the emanation to be 222 to 222 '4. These two give 

 values of S = 361'80w 2 as between 1783'! and 1789'5, with the probability that it is 

 close to 1783. The uncertainty in the value of the constant 361 '80 will not affect 

 this. 



An examination of the spectrum for constant separations shows a large number of 

 triplets with Vl in the region 5371 to 5383 and v 2 at 2671 and less. Further, the 

 higher values appear in sets which show inverted order of intensities. This suggests 

 that the lines belong to D satellite systems and that the separations about 5383, 2671 



3 M 2 



